1. Field of the Invention
This invention relates to a mechanism for opening and closing an openable apparatus and more particularly to a mechanism for opening and closing an openable apparatus, such as a copying machine, a printer, a facsimile machine and the like, which has a lower body portion and an upper body portion pivotally supported at a pivotal shaft at one of its ends by the lower body portion and opened and closed by the pivotal movement about the pivotal shaft.
2. Description of the Related Art
Generally, a shell type openable apparatus such as a copying machine, a printer and a facsimile machine is designed to have an upper body portion and a lower body portion and to enable the upper body portion to rotate about an pivotal axis at one of its ends so as to be opened and closed with respect to the lower body portion. When the openable apparatus is operated, maintained or checked, the upper body portion is opened.
In FIG. 5 is shown a printer used as an image formation device having an opening and closing function as an example of the conventional apparatus, the upper body portion of which is adapted to be opened and closed. The printer 1 comprises a lower body portion 2 and an upper body portion 3 provided separately from the lower body portion 2. The upper body portion 3 is opened by being rotated upward about a pivotal shaft 4 provided at one end of the upper body portion 3 to the position as shown by a two-dot chain line. This opening function facilitates the maintenance of the inner structure of the image formation device, the removal of a jammed paper sheet or the like.
Many functional components are housed in the lower body portion 2 of the printer 1, and an image formation head 5 is provided in the upper body portion 3 in such a manner that the head 5 faces an image formation drum 6 provided in the lower body portion 2 when the upper body portion 2 is closed, as shown by a solid line in FIG. 5.
In the conventional printer 1, however, the opening angle of the upper body portion 3 is generally set to less than 90.degree., with the result that the center of gravity of the opened upper body portion 3 is positioned so that the upper body portion 3 is biased in the closed direction, entailing a danger due to the closing of the upper body portion 3.
In this prior art, therefore, it is not easy to maintain the components (such as a unit having the image formation drum 6 as the main element) densely arranged in the lower body portion 2, due to the fact that a wide opening angle of the upper body portion 3 is not available.
When a one-way type rotary oil damper is used in this prior art, the upper body portion 3 is opened smoothly and is closed slowly. This feature exhibits a good operativeness of the upper body portion 3.
Since, however, the pivotal shaft 4 which is a center of rotation of the upper body portion 3 is provided at one end of the printer body 1, the use of the oil damper cannot make the opening angle of the upper body portion 3 equal to or more than 90.degree.. This makes it difficult to perform maintenance of the printer such as the removal of a jammed paper sheet and the supply of a toner (a developer).
In order to widen the opening angle of the upper body portion 3 by using a one-way type rotary oil damper, a printer having a structure as shown in FIG. 6 can be used.
A printer 7 having the similar structure to that of the printer as shown in FIG. 5 comprises a lower body portion 8, an upper body portion 10 provided rotatably about a pivotal shaft 9 so as to be opened and closed, and a one-way type rotary oil damper 12 provided in the upper body portion 10 and engaging with a segmental gear 11 provided in the lower body portion 8.
In order to widen the opening angle to more than 90.degree., however, the upper body portion 10 must be provided with an extension 13 on which the rotary oil damper 12 is mounted, resulting in a complicated structure of the upper body portion 10. This structure has the disadvantage that it requires a high assembling cost.
Further, the one-way type rotary oil damper 12 resists against the force of the upper body portion 10 when the portion 10 is closed, that is, when it is rotated in the counterclockwise direction in FIG. 6, but the damper 12 little resists against the force of the upper body portion 10 when the portion 10 is opened, that is, when it is rotated in the clockwise direction in FIG. 6. When the upper body portion 10 passes the dead point right over the pivotal point 9 and then arrives at the fully opened position in the course of the opening of the portion 10, the weight of the upper body portion 10 acts in the direction in which the portion 10 is further opened. Since the oil damper 12 little resists against the opening force of the upper body portion 10, as explained above, the shock is directly applied to a stop for limiting the portion 10 to the opening position without being suppressed when the portion 10 is raised forcibly from the closed position, and the stop and/or a vicinity portion close thereto is liable to be broken.
On the other hand, in order to close the upper body portion 10, there are difficulties that the heavy portion 10 must be raised from the opened position to the dead point and the resistance of the rotary oil damper 12 against the rotation of the portion 10 prevents the portion 10 from moving downward smoothly.
Accordingly, where the one-way type rotary oil damper is used for opening and closing the conventional shell type openable apparatus, the above-mentioned problems arises when the apparatus is opened and closed.